Power supply system, multiple dwelling, and computer program

ABSTRACT

A power supply system for supplying power to a plurality of loads includes a plurality of fuel cells for generating and supplying power to be supplied to the respectively corresponding loads, wherein the fuel cells are provided to correspond to the plurality of loads, a power network for receiving surplus power, which is generated ‘by the fuel cells except power to be supplied to the loads corresponding to the fuel cells, and supplying the surplus power to the loads short of power, wherein the power network is coupled to the plurality of fuel cells, and a control unit for stopping power generation of a first fuel cell among the fuel cells corresponding to a first load among the loads and controlling a second fuel cell among the fuel cells to generate power to be supplied to the first load as the surplus power if an amount of power to be supplied to the first load is less than a predetermined first threshold.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of, and claims thepriority benefit of, U.S. application Ser. No. 10/898,639 filed on Jul.23, 2004, now U.S. Pat. No. 7,518,262 which claims benefit of U.S.Provisional Application No. 60/489,761, filed on Jul. 23, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply system for supplyingpower to a plurality of loads, a multiple dwelling including the powersupply system, and a computer program for allowing the power supplysystem to be in operation.

2. Description of the Related Art

Conventionally, there is a power supply system of a distribution type inwhich its power sources are distributed and disposed corresponding tothe loads to which power is supplied. In the above power supply systemof the distribution type, each of the power sources supplies power toonly the corresponding load.

In the conventional power supply system of the distribution type,however, since each of the power sources supplies power to only thecorresponding load, it cannot supply power to the corresponding load ifit stops working due to a breakdown or maintenance. Moreover, in orderto prevent the stoppage of power supply, if each of the loads is alwayscoupled to a power system (hereinafter, referred to as a “system”) suchas a commercial power supply, the cost of the facilities becomes high.Particularly, if loads in the mountains or isolated islands are suppliedwith power, the cost for the connection to the system increasessignificantly.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a powersupply system, a multiple dwelling, and a computer program, which iscapable of overcoming the above drawbacks accompanying the conventionalart. The above and other objects can be achieved by combinationsdescribed in the independent claims. The dependent claims define furtheradvantageous and exemplary combinations of the present invention.

According to the first aspect of the present invention, a power supplysystem for supplying power to a plurality of loads includes a pluralityof fuel cells for generating and supplying power to be supplied to therespectively corresponding loads, wherein the fuel cells are provided tocorrespond to the plurality of loads, a power network for receivingsurplus power, which is generated by the fuel cells except power to besupplied to the loads corresponding to the fuel cells, and supplying thesurplus power to the loads short of power, wherein the power network iscoupled to the plurality of fuel cells, and a control unit for stoppingpower generation of a first fuel cell among the fuel cells correspondingto a first load among the loads and controlling a second fuel cell amongthe fuel cells to generate power to be supplied to the first load as thesurplus power, if an amount of power to be supplied to the first load isless than a predetermined first threshold.

The control unit may control the first fuel cell, of which powergeneration has been stopped, to generate power to be supplied to thefirst load and stop the second fuel cell from generating the surpluspower, if the surplus power supplied from the power network to the firstload is more than a second threshold greater than the first threshold.

The control unit may control a third fuel cell among the fuel cellscorresponding to a third load among the loads, which is already inoperation, to generate power as the surplus power required for a fourthload among the loads to start to be in operation. In this case, thecontrol unit may control a fourth fuel cell among the fuel cellscorresponding to the fourth load to generate power to be supplied to thefourth load and stop the third load from generating the surplus powerfrom the time when a predetermined period elapses after the fourth loadstarts to be in operation.

The control unit may stop power generation of a fifth fuel cell amongthe fuel cells corresponding to a fifth load among the loads and controla sixth load among the loads to generate power to be supplied to thefifth load as the surplus power, if an average value of power consumedby the fifth load during a predetermined past period is less than thefirst threshold.

The control unit may decrease an amount of power generated by a seventhfuel cell among the fuel cells, if the amount of power generated by theseventh fuel cell is more than an average value of power, which has beenconsumed by a seventh load among the loads corresponding to the seventhfuel cell during a predetermined past period, as much as a predeterminedvalue. The control unit may increase an amount of power generated by aneighth fuel cell among the fuel cells, if an average value of power,which has been received by an eighth load among the loads correspondingto the eighth fuel cell from the power network during a predeterminedpast period, is more than a predetermined value.

The power supply system may further include a capacitor for storingelectric charge equivalent to a portion of the surplus power supplied tothe power network except power supplied to the loads and supplying thepower stored to the loads if a total amount of power required by theplurality of loads is more than a total amount of power which can begenerated by the plurality of fuel cells, wherein the control unit mayincrease the amount of power generated by the plurality of fuel cells,if the power stored by the capacitor is less than a predetermined value.The power generation efficiency of the plurality of fuel cells mayincrease according to an amount of power generated by the plurality offuel cells.

According to the second aspect of the present invention, a computerprogram for instructing a power supply system to supply power to aplurality of loads, wherein the power supply system includes a pluralityof fuel cells for generating and supplying power to be supplied to therespectively corresponding loads, wherein the fuel cells are provided tocorrespond to the plurality of loads, a power network for receivingsurplus power, which is generated by the fuel cells except power to besupplied to the loads corresponding to the fuel cells, and supplying thesurplus power to the loads short of power, wherein the power network iscoupled to the plurality of fuel cells, and a control unit for stoppingpower generation of a first fuel cell among the fuel cells correspondingto a first load among the loads and controlling a second fuel cell amongthe fuel cells to generate power to be supplied to the first load as thesurplus power, if an amount of power to be supplied to the first load isless than a predetermined first threshold. The power generationefficiency of the plurality of fuel cells may increase according to anamount of power generated by the plurality of fuel cells.

According to the third aspect of the present invention, a multipledwelling provided with a plurality of dwelling units includes aplurality of fuel cells for generating and supplying power to besupplied to the respectively corresponding dwelling units, wherein thefuel cells are provided to correspond to the plurality of dwellingunits, a power network for receiving surplus power, which is generatedby the fuel cells except power to be supplied to the dwelling unitscorresponding to the fuel cells, and supplying the surplus power to thedwelling units short of power, wherein the power network is coupled tothe plurality of fuel cells, and a control unit for stopping powergeneration of a first fuel cell among the fuel cells corresponding to afirst dwelling unit among the dwelling units and controlling a secondfuel cell among the fuel cells to generate power to be supplied to thedwelling unit as the surplus power, if an amount of power to be suppliedto the first dwelling unit is less than a predetermined first threshold.The power generation efficiency of the plurality of fuel cells mayincrease according to an amount of power generated by the plurality offuel cells.

The summary of the invention does not necessarily describe all necessaryfeatures of the present invention. The present invention may also be asub-combination of the features described above. The above and otherfeatures and advantages of the present invention will become moreapparent from the following description of the embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of the configuration of a multiple dwelling 100according to an exemplary embodiment of the present invention.

FIG. 2 shows an example of the power generation efficiency of the fuelcells (30 a to 30 c).

FIGS. 3A and 3B show an example of the power consumed by the loads (40 ato 40 c).

FIG. 3A shows an example of the amount of power consumed and the amountof power generated, and FIG. 3B shows another example thereof.

FIG. 4 shows another embodiment of the power supply system 10.

FIG. 5 shows an example of the configuration of a computer 200 forcontrolling the power supply system 10.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on the preferred embodiments,which do not intend to limit the scope of the present invention, butexemplify the invention. All of the features and the combinationsthereof described in the embodiment are not necessarily essential to theinvention.

FIG. 1 shows an example of the configuration of a multiple dwelling 100according to an exemplary embodiment of the present invention. Themultiple dwelling 100 includes a plurality of dwelling units (60 a to 60c) and a power supply system 10. The power supply system 10 suppliespower to a plurality of loads (40 a to 40 b) provided in the pluralityof dwelling units (60 a to 60 c).

The power supply system 10 includes a plurality of fuel cells (30 a to30 c), a power network 20, and a control unit 50. The plurality of fuelcells (30 a to 30 c), each of which is provided to correspond to theplurality of loads (40 a to 40 c), generates and supplies power to thecorresponding loads (40 a to 40 c). Each of the fuel cells (30 a to 30c) may generate power according to the power to be consumed by thecorresponding loads (40 a to 40 c) or a predetermined amount of power.

The power network 20, which is coupled to the plurality of the fuelcells (30 a to 30 c), receives surplus power, which is generated by theplurality of the fuel cells (30 a to 30 c) except the power supplied tothe corresponding loads (40 a to 40 c). Moreover, the power network 20supplies the surplus power received to the loads (40 a to 40 c) short ofpower. That is, the power network 20 receives the surplus power from anyof the fuel cells (30 a to 30 c), which generate power more than thatconsumed by the corresponding loads (40 a to 40 c), and supplies powerto any of the loads (40 a to 40 c), which consume power more than thatgenerated by the corresponding fuel cells (30 a to 30 c).

Moreover, the control unit 50 controls the amount of power generated byeach of the fuel cells (30 a to 30 c) so that the power generationefficiency of each of the fuel cells (30 a to 30 c) can be high. Thecontrol unit 50 will be described in detail hereinafter.

By the above configuration, each of the loads (40 a to 40 c) can besupplied with power from the plurality of fuel cells (30 a to 30 c), soit is possible to improve the reliability of power supply. For example,although any of the fuel cells (30 a to 30 c) cannot generate power dueto a breakdown or maintenance, the loads (40 a to 40 c) can be suppliedwith power from the corresponding fuel cells.

Moreover, it is extremely rare that all of the loads (40 a to 40 c)needs the maximum power (peak power) at the same time, so when one ofthe loads (40 a to 40 c) consumes the peak power, the fuel cells (30 ato 30 c) corresponding to the other loads (40 a to 40 c) may make up forthe power of the load. Accordingly, even if all of the fuel cells (30 ato 30 c) cannot generate the peak values of the power consumed by thecorresponding loads (40 a to 40 c), power supply can be stablyperformed. According to this embodiment, by coupling the plurality offuel cells (30 a to 30 c) to each other, it is possible to reduce thetotal power generation capacity of the plurality of fuel cells (30 a to30 c). Accordingly, it is possible to provide a low-cost power supplysystem, of which the reliability of power supply is high even if it isdisconnected to the system. Therefore, it is possible to provide thepower supply system with high reliability at low cost even in the placeswhere it is geographically difficult to be in connection with the systemor the cost for the communication is high, e.g. isolated islands.

Moreover, the total power generation capacity of the plurality of fuelcells (30 a to 30 c) is given by C×N, where C is the power generationcapacity of each of the fuel cells (30 a to 30 c) and N is the number ofthe fuel cells (30 a to 30 c) provided. The probability in case that thepower supply is insufficient is represented by EM(N)>C×N×(1−R), where Ris the probability of the breakdown of the fuel cells (30 a to 30 c) andEM(N) indicates the maximum total power consumed by the plurality ofloads (40 a to 40 c). In this embodiment, it is preferable that thepower generation capacity and the number of the fuel cells (30 a to 30c) provided should be set so that the probability in case that the powersupply is insufficient is less than the probability in case that thepower generation of the system stops. Accordingly, it is possible tohave the reliability of power supply equal to the system or higher.

FIG. 2 shows an example of the power generation efficiency of the fuelcells (30 a to 30 c). In FIG. 2, the horizontal axis represents theamount of the power generated by the fuel cells and the vertical axisrepresents the power generation efficiency of the fuel cells. As shownin FIG. 2, the power generation efficiency increases according to theamount of the power generated. Accordingly, it is preferable that thecontrol unit 50 controls the fuel cells (30 a to 30 c) in such a mannerthat each of the fuel cells (30 a to 30 c) generates power more than apredetermined amount.

FIGS. 3A and 3B show an example of the power consumed by the loads (40 ato 40 c). Although the fuel cells (30 a to 30 c) generate poweraccording to the power consumed by the corresponding loads (40 a to 40c), the power generation efficiency of the fuel cells (30 a to 30 c) islow in a region where the amount of power generated is small as shown inFIG. 2.

As shown in FIG. 3A, when the amount of the power to 30 be supplied toone of the loads 40 a, that is, the power consumed by the load 40 a isless than a predetermined first threshold, the control unit 50 stops thepower generation of the fuel cell 30 a corresponding to the load 40 aand controls other fuel cells (30 b and 30 c) to generate the power tobe supplied to the load 40 a as the surplus power. In this case, thecontrol unit 50 may select one or more fuel cells (the fuel cell 30 b inthis embodiment 30 b) capable of generating the power to be suppliedamong other fuel cells (30 b and 30 c) on the basis of a sequence that afuel cell, of which amount of power generated is large, is firstselected, and control the fuel cell(s) to perform power generation.Accordingly, it is possible to prevent the fuel cells (30 a to 30 c)from generating power in the region where the efficiency is low andimprove the power generation efficiency of the entire fuel cells (30 ato 30 c).

Moreover, as shown in FIG. 3B, when the amount of the surplus powersupplied from the power network 20 to the load 40 a corresponding to thefuel cell 30 a, of which power generation has been stopped, that is, thepower consumed by the load 40 a is more than a predetermined secondthreshold greater than the first threshold, the control unit 50 maycontrol the fuel cell 30 a, of which power generation has been stopped,to generate the power to be supplied to the load 40 a and stop otherfuel cells (30 b and 30 c) from generating the surplus power. Forexample, in case of a load driven by the amount of power near the firstthreshold, if the stop/start of power generation of the fuel cells isdetermined only by the first threshold, the stop/start of powergeneration of the fuel cells is frequently repeated, thereby the powergeneration efficiency of the fuel cells becomes low. However, accordingto the example described in connection with FIG. 3, the repetition ofthe stop/start of power generation of the fuel cells (30 a to 30 c) isreduced, and thus the power generation efficiency of the fuel cells (30a to 30 c) can be improved.

Moreover, when the average value of the power consumed by, for example,one of the loads 40 a during a predetermined past period is less thanthe first threshold, the control unit 50 may stop the fuel cell 30 acorresponding to the load 40 a from generating power and controls otherfuel cells (30 b and 30 c) to generate the power to be supplied to theload 40 a as the surplus power. Moreover, when the average value of thesurplus power supplied from the power-network 20 to the load 40 acorresponding to the fuel cell 30 a, of which power generation has beenstopped, during a predetermined past period is less than the firstthreshold, the control unit 50 may control the fuel cell 30 a, of whichpower generation has been stopped, to generate the power to be suppliedto the load 40 a and stop other fuel cells (30 b and 30 c) fromgenerating the surplus power. Also in this case, the repetition of thestop/start of power generation of the fuel cells (30 a to 30 c) isreduced, and thus the power generation efficiency can be improved.

Moreover, the response of the fuel cell to the change of the powerconsumed is slow. Particularly, the response to the change of the powerconsumed while the load starts to be in operation might be slow.Accordingly, the control unit 50 may control, for example, the fuelcells (30 b and 30 c) corresponding to the loads (40 b and 40 c), whichare already in operation, to generate power required for the load 40 ato starts to be in operation as the surplus power. In this case, thecontrol unit 50 may control the fuel cell 30 a corresponding to the load40 a to generate the power to be supplied to the load 40 a and stopother fuel cells (30 b and 30 c) from generating the surplus power fromthe time when a predetermined period elapses after the load 40 a startsto be in operation. By this control, the response of power supply can beimproved.

Moreover, when the amount of the power generated by one of the fuelcells (30 a to 30 c) is more than the power consumed by correspondingone of the loads (40 a to 40 c) during a predetermined past period asmuch as a predetermined value, the control unit 50 may decrease theamount of the power generated by the corresponding fuel cell. Moreover,when the average value of the power received by one of the loads (40 ato 40 c) from the power network 20 during a predetermined past period ismore than a predetermined value, the control unit 50 may increase theamount of the power generated by corresponding one of the fuel cells (30a to 30 c). In this way, by controlling the amounts of the powergenerated by the fuel cells (30 a to 30 c) based on the average valuesof power consumed during a predetermined past period, it is possible tocontrol the changes of the amounts of the power generated by the fuelcells (30 a to 30 c) and perform stable power generation.

Moreover, the control unit 50 may select one or more 30 of the fuelcells (30 a to 30 c) capable of generating the total power consumed bythe plurality of loads (40 a to 40 c) and control the fuel cell(s)selected to generate the total power consumed. That is, the control unit50 selects one or more of the fuel cells (30 a to 30 c) capable ofgenerating the total power consumed, when the fuel cell(s) to beselected generate power at the maximum efficiency. By this control, itis also possible to improve the power generation efficiency of theentire fuel cells (30 a to 30 c).

FIG. 4 shows another embodiment of the power supply system 10. In thisembodiment, the power network 20 of the power supply system 10 iscoupled to an external power source. When the total amount of the powerconsumed by the plurality of loads (40 a to 40 c) is more than the totalpower generation capacity of the plurality of fuel cells (30 a to 30 c),the power network 20 receives the insufficient power from the externalpower source and supplies it to the loads (40 a to 40 c).

Here, the external power source may be another power supply system 10 ora capacitor. If the external power source is another power supply system10, the power networks 20 of the power supply systems 10 are coupled toeach other and perform power transfer. In this way, as the power supplysystem 10 is coupled to another power supply system 10, the reliabilityof power supply can be further improved.

Moreover, if the external power source is a capacitor, the capacitorstores electric charge equivalent to a portion of the surplus powersupplied from the fuel cells (30 a to 30 c) to the power network 20except the power supplied to the loads (40 a to 40 c) and supplies thepower stored to the plurality of loads (40 a to 40 c) when the totalpower needed by the plurality of loads (40 a to 40 c) is more than thetotal amount of the power generated by the plurality of fuel cells (30 ato 30 c). In the above configuration, the reliability of power supplycan be further improved also. In this case, when the power stored in thecapacitor is less than a predetermined value, it is preferable that theamount of the power generated by the plurality of fuel cells (30 a to 30c) is increased and the power is stored in the capacitor. The controlunit 40 may calculate the amount of the electric charge to be stored inthe capacitor based on the total amount of the power generated by theplurality of fuel cells (30 a to 30 c) and the total amount of the powersupplied to plurality of loads (40 a to 40 c) during a predeterminedpast period.

FIG. 5 shows an example of the configuration of a computer 200 forcontrolling the power supply system 10. In this embodiment, the computer200 stores a computer program for instructing the power supply system 10to function as described in connection with FIGS. 1 to 4. The computer200 includes a CPU 700 a ROM 702, a RAM 704, a communication interface706, a hard disk drive 710, a FD disk drive 712, and a CD-ROM drive 716.The CPU 700 operates based on the computer program stored in the ROM702, the RAM 704, a hard disk 710, an FD disk 714 and/or a CD-ROM 718.

For example, the computer program instructing the power supply system 10to function instructs the power supply system 10 to function as thepower network 20, the plurality of fuel cells (30 a to 30 c) and thecontrol unit 50 described in connection with FIGS. 1 to 4. Moreover, thecomputer 200 may function as the control unit 50 based on the computerprogram.

The communication interface 706 communicates with the power supplysystem 10. The hard disk drive 710 as an example of the storing devicestores the setting information and the computer program for theoperation of the CPU 700. The ROM 702, the RAM 704 and/or the hard diskdrive 710 store the computer program instructing the power supply system10 to function as described in connection with FIGS. 1 to 4. Moreover,the computer program may be stored in a flexible disk 720, a CD-ROM 722,a hard disk drive 710, etc.

The FD drive 712 reads the computer program from the flexible disk 714and provides it to the CPU 700. The CD-ROM drive 706 reads the computerprogram from the CD-ROM 718 and provides it to the CPU 700.

Moreover, although the computer program is retrieved from a recordingmedium and transferred directly to the RAM to be performed, it may beretrieved and transferred to the RAM after being installed in the harddisk drive in advance. Further, the computer program may be stored inone recording medium or more. Moreover, the computer program stored in arecording medium may provide its functions together with an operatingsystem. For example, the computer program may request the operatingsystem to perform all or a part of the functions and provide itsfunctions based on the response from the operating system.

As the recording medium for storing the computer program, there can be,in addition to the flexible disk, the CD-ROM, etc., an optical recordingmedium such as a DVD, a PD, etc., an electro-optical recording mediumsuch as MD disc, a tape medium, a magnetic medium, and a semiconductormemory such as an IC card, a miniature card, etc.

In addition, a storage device such as a hard disc drive or RAM providedin a server system connected to a dedicated communication network orInternet may be used as the recording medium.

As obvious from the description above, according to the presentinvention, it is possible to provide a power supply system, in which thereliability of power supply is high and the cost is low, withoutconnection with a system.

Although the present invention has been described by way of exemplaryembodiments, it should be understood that those skilled in the art mightmake many changes and substitutions without departing from the spiritand the scope of the present invention which is defined only by theappended claims.

1. A power supply system for supplying power to a plurality of loads,comprising: a plurality of fuel cells for generating and supplying powerto be supplied to said respectively corresponding loads, wherein saidfuel cells are provided to correspond to said plurality of loads; apower network for receiving surplus power, which is generated by saidfuel cells except power to be supplied to said loads corresponding tosaid fuel cells, and supplying said surplus power to said loads short ofpower, wherein said power network is coupled to said plurality of fuelcells; and a control unit for stopping power generation of a first fuelcell among said fuel cells corresponding to a first load among saidloads and controlling other fuel cells among said fuel cells to generatepower to be supplied to said first load as said surplus power via apower network, if an amount of power to be supplied to said first loadis less than a predetermined first threshold.
 2. The power supply systemas claimed in claim 1, wherein said control unit controls said firstfuel cell, of which power generation has been stopped, to generate powerto be supplied to said first load and stops said other fuel cells fromgenerating said surplus power if said surplus power supplied from saidother fuel cells via said power network to said first load is more thana second threshold greater than said first threshold.
 3. The powersupply system as claimed in claim 1, wherein said control unit controlsa fuel cell among said other fuel cells corresponding to a load amongsaid loads, which is already in operation, to generate power as saidsurplus power required for the load, which is already in operation,among said loads to start to be in operation.
 4. The power supply systemas claimed in claim 3, wherein said control unit controls a fuel cellamong said other fuel cells corresponding to said load, which is alreadyin operation, and stops said fuel cell from generating said surpluspower from said time when a predetermined period elapses after said loadstarts to be in operation.
 5. The power supply system as claimed inclaim 1, wherein said control unit stops power generation of said firstfuel cell and controls said other fuel cells to generate power to besupplied to said first load as said surplus power, if an average amountof power consumed by said first load during a predetermined past periodis less than said first threshold.
 6. The power supply system as claimedin claim 1, wherein said control unit decreases an amount of powergenerated by said first fuel cell if said amount of power generated bysaid first fuel cell is more than an average amount of power that hasbeen consumed by said first load during a predetermined past period. 7.The power supply system as claimed in claim 1, wherein said control unitincreases an amount of power generated by said first fuel cell if anaverage amount of power that has been received by said first load fromsaid other fuel cells via said power network during a predetermined pastperiod is more than a predetermined value.
 8. The power supply system asclaimed in claim 1 further comprising a capacitor for storing electriccharge equivalent to a portion of said surplus power supplied to saidpower network except power supplied to said loads and supplying saidpower stored to said loads if a total amount of power required by saidplurality of loads is more than a total amount of power which can begenerated by said plurality of fuel cells, wherein said control unitincreases said amount of power generated by said plurality of fuel cellsif said power stored by said capacitor is less than a predeterminedvalue.
 9. The power supply system as claimed in claim 1, wherein powergeneration efficiency of said plurality of fuel cells increasesaccording to an amount of power generated by said plurality of fuelcells.
 10. A non-transitory computer readable medium storinginstructions for instructing a power supply system to supply power to aplurality of loads, wherein said power supply system comprises: aplurality of fuel cells for generating and supplying power to besupplied to said respectively corresponding loads, wherein said fuelcells are provided to correspond to said plurality of loads; a powernetwork for receiving surplus power, which is generated by said fuelcells except power to be supplied to said loads corresponding to saidfuel cells, and supplying said surplus power to said loads short ofpower, wherein said power network is coupled to said plurality of fuelcells; and a control unit for stopping power generation of a first fuelcell among said fuel cells corresponding to a first load among saidloads and controlling other fuel cells among said fuel cells to generatepower to be supplied to said first load as said surplus power via apower network, if an amount of power to be supplied to said first loadis less than a predetermined first threshold.
 11. A non-transitorycomputer readable medium as claimed in claim 10, wherein powergeneration efficiency of said plurality of fuel cells increasesaccording to an amount of power generated by said plurality of fuelcells.
 12. A multiple dwelling provided with a plurality of dwellingunits, comprising: a plurality of fuel cells for generating andsupplying power to be supplied to said respectively correspondingdwelling units, wherein said fuel cells are provided to correspond tosaid plurality of dwelling units; a power network for receiving surpluspower, which is generated by said fuel cells except power to be suppliedto said dwelling units corresponding to said fuel cells, and supplyingsaid surplus power to said dwelling units short of power, wherein saidpower network is coupled to said plurality of fuel cells; and a controlunit for stopping power generation of a first fuel cell among said fuelcells corresponding to a first dwelling unit among said dwelling unitsand controlling other fuel cells among said fuel cells to generate powerto be supplied to said dwelling unit as said surplus power via a power anetwork, if an amount of power to be supplied to said first dwellingunit is less than a predetermined first threshold.
 13. The multipledwelling as claimed in claim 12, wherein power generation efficiency ofsaid plurality of fuel cells increases according to an amount of powergenerated by said plurality of fuel cells.